Scanners are capable of higher resolution measurement in comparison with spectrocolorimeters so that scanners can capture not only color charts but also various kinds of image, and are expected to be used for color management of various kinds of image other than color charts. Color management is performed on the basis of device-independent color values, but device-independent color values are not given by just using a scanner. Therefore, color management using a scanner is performed by using a scanner profile. A scanner profile is created by the following operations. A printer prints a chart (color chart) including an array of color patches and the chart is measured with a scanner and a spectrocolorimeter. Measured values of the patches taken with the scanner (for example, RGB values) are associated with corresponding measured values of the patches taken with the spectrocolorimeters (for example, L*a*b* values in the CIE 1976 color space, XYZ values in the CIE 1931 color space. L*u*v* values in the CIE 1976 color space or CIECAM02 values), which are referred to as colorimetric values, to create a scanner profile.
Scanner profiles are used under the assumption that scanners output measured values with consistency during their usable time. However, measurements with a scanner sometimes lack consistency because of a change of the performance of the scanner with age and/or a change of the environmental condition, and it is preferable that a scanner profile is timely corrected. As an example of a technique relating to a correction of a scanner profile, Japanese Unexamined Patent Publication (JP-A) No. 2017-069855 discloses the following technique. The technique uses a controller that causes a print engine to print a first color chart and a second color chart including color patches of specific colors being on the edge of a color gamut of a printer, and causes an in-line scanner and an in-line colorimeter to obtain RGB values and colorimetric values of color patches of each of the first color chart and the second color chart. The controller creates a scanner profile by associating the RGB values and the colorimetric values of each of the color patches of the first color chart with each other. The controller determines a first color gamut of the printer by using one or both of the RGB values and the colorimetric values of the color patches of the first color chart, and further determines a second color gamut of the printer by using one or both of the RGB values and the colorimetric values of the color patches of the specific colors in the second color chart. The controller then corrects a scanner profile on the basis of a comparison results of the first color gamut and the second color gamut of the printer.
As an example of a technique relating to timely performing a correction, JP-A No. 2010-137474 discloses the following image forming apparatus. The image forming apparatus includes a recording head for forming an image on a recording medium, and a color-correction processor that performs a color correction of an input image data. The image forming apparatus further includes an image-output controller that controls the recording head according to the image data given after the color correction in such a manner that the image corresponding to the image data is formed on the recording medium. The image forming apparatus further includes a patch-forming controller that controls the recording head so as to form patches for color measurement, on the recording medium, and a memory device for storing output conditions for forming the image and measurement results of the patches for color measurement formed under the output conditions. The image forming apparatus further includes a correction-data updater that changes correction data to be used for the color correction to be performed by the color-correction processor, when a difference between a first measurement result and a second measurement result of the patches for color measurement exceeds a predetermined acceptable range, where the first measurement result is a measurement result of the patches for color measurement, obtained by forming and measuring the patches for color measurement, before starting of a print job or during processing of the print job, and the second measurement result is a measurement result of the patches for color measurement, stored in the memory device.
As disclosed in JP-A No. 2017-069855, a correction of a scanner profile uses a process of printing a color chart by a printer, and if a need for correction of a scanner profile arises during job processing, the job processing is suspended through the process of printing a color chart, in order to correct the scanner profile during the job processing. In view of that, a conventional system is configured to monitor the number of printed sheets or the time elapsed from the prior correction, and print a color chart at the end of processing of a certain job after a judgement that the number of printed sheets or the time elapsed from the prior correction exceeds a predetermined threshold.
Further, JP-A No. 2010-137474 discloses the technique to perform a test printing (print a proof) before actual printing (perform pressrun). In the test printing, the apparatus in the JP-A No. 2010-137474 creates patches for color measurement in a blank space (a non-image area) of a recording medium, measures the patches for color measurement with an in-line detector (an RGB array sensor), and changes correction data to be used for color correction in response to a judgement that a difference between a result of the measurement obtained and a result of the measurement stored in the memory device exceeds a predetermined acceptable range.
However, when processing a job containing a large amount of pages in the system configured to monitor printed matters continuously, measured values taken by a scanner can be inconsistent during printing a large amount of pages, and under such a situation, it is difficult to correct a scanner profile appropriately with the above-described technique to print a color chart at the end of processing of a job. Further, with the technique to arrange patches in a blank space of a sheet for test printing as disclosed in JP-A No. 2010-137474, it is difficult to arrange all the patches necessary for a correction of a scanner profile, in the blank space. Further, in a technique using the apparatus configured to measure patches with an in-line scanner as a disclosed in JP-A No. 2010-137474, patches can be arranged in margins at the upper, bottom, right and left ends of a printing sheet. However, in a case that an apparatus configured to measure patches with an inline scanner and an in-line spectrocolorimeter is used for the technique, it is necessary to place patches in a restricted part in the blank space (margins), which can be measured with the in-line spectrocolorimeter. It makes more difficult to arrange all the patches necessary for a correction of a scanner profile, in the blank space of a recording medium.